In the field of explosives, high strength detonating cord and low strength detonating cord are being rapidly replaced by energy transmission devices which have little or no brisance. These signal devices have the advantage of increased safety and lower noise levels making them particularly desirable for blasting operations close to populated areas. Such a signal transmission tube is disclosed in U.S. Pat. No. 4,290,366. Another fuse device is disclosed in U.S. Pat. No. 3,590,739.
A disadvantage of the tube utilized in construction of the signal transmission device such as that shown in U.S. Pat. No. 4,290,366 is that the signal tube which loosely contains the reactive element may be deformed longitudinally a substantial length. In contrast, the reactive element inside the fuse tube has little elasticity. As a result, in a borehole, and particularly a borehole filled with warm explosives, the tube may stretch a considerable length; whereas, the reactive element contained in the fuse tube does not stretch much. As a result the blasting cap provided at the end of the tube may move away from the end of the reactive element contained within the tube. This can create a gap between the end of the reactive element and the receptacle end of the blasting cap. As a result of this separation the reliability of the fuse and cap assembly may decrease and it may fail to initiate the cap. Any reduction in reliability of the assembly is undesired.
U.S. Pat. No. 4,493,261 addresses the problem of the stretching and breaking of fuse tubes such as used in a construction of a device disclosed in U.S. Pat. No. 3,590,739 by the incorporation therein of a plurality of textile filaments positioned between an inner tube over which is laid the textile filaments followed by the extrusion of a second outside tube over the inside tube and filaments. This construction has the disadvantage of being complex to form by requiring several extrusion steps and also having difficulties in achieving good quality bonds between the inner tube, the outer tube, and the filaments bonded therebetween. Further such a process usually has slow rates of productions because two or more extrusion steps are needed.
In contrast, the present invention provides an apparatus and method for the selective placement of one or more reinforcing yarns in an extruded signal tube in one step. This is advantageous in terms of both economics and also in achieving a good bond between the reinforcing yarn(s) and the tube wall. Also, it is advantageous because it allows a minimal wall thickness to be used while preventing blow outs of the tube wall from the reaction of the reactive filament by the selective placement of the yarns in the tube wall. The single step process of the invention can be performed while maintaining high production rates.